1. Field of the Invention
The present invention relates to multiplex transmitter-receiver systems for transmitting and/or receiving a plurality of signals through a single transmission line. The term "transmitter-receiver system", as used herein, refers to a system adapted for at least either or both of the transmission and receiving of signals.
2. Description of the Related Art
FIG. 27 schematically shows two transmitter-receiver systems 2 and 3 connected to a three-phase a.c. power supply 1 and interconnected by a single signal transmission line 5.
The first transmitter-receiver system 2 is used specifically for transmitting signals (transmitter), and the second transmitter-receiver system 3 for receiving signals (receiver). These systems are disclosed, for example, in Unexamined Japanese Patent Publications SHO 51-78112.
The transmitter 2 comprises a synchronizing signal generating circuit 4 for producing six transmission synchronizing signals from a three-phase alternating current, and a transmission circuit (transmission signal processing circuit) 6 for transmitting a plurality of signals as selected from among these synchronizing signals through the single transmission line 5. The receiver 3 comprises a synchronizing signal generating circuit 7 for producing six receiving synchronizing signals from the three-phase alternating current like the circuit 4, and a receiving circuit (receiving signal processing circuit ) 8 for receiving a plurality of signals through the single transmission line 5 based on these synchronizing signals. The synchronizing signal generating circuits 4, 7 of the transmitter 2 and the receiver 3 respectively comprise signal a.c. power supply circuits 10, 11 for obtaining three signal a.c. power supplies from the three-phase alternating current using a transformer, and diode matrix circuits 12, 13 for producing six synchronizing signals by clipping these three signal a.c. power supplies with signal a.c. power supplies which are different from one another by 120 degrees in phase and taking out the superposed portions of the waveforms.
However, the conventional transmitter-receiver systems 2, 3 described above require a transformer for the signal a.c. power supply circuits 10, 11 of the circuits 4, 7, and are therefore large-sized and heavy. Further since the diode matrix circuits 12, 13 produce six synchronizing signals from the three a.c. power supplies, the systems are limited in the number of synchronzing signals producible and accordingly in the number of signals which can be transmitted through the single transmission line 5. Furthermore, the synchronizing signals are not available with high accuracy owing to the distortion of waveforms since the synchronizing signals are afforded by the a.c. power supplies.